Engine systems may use EGR (exhaust gas recirculation) to address exhaust NOx emissions. For example, EGR systems may divert exhaust gas from upstream of an exhaust turbine to downstream of an intake compressor, or from downstream of an exhaust turbine to upstream of an intake compressor. Various approaches may be used to control EGR systems and coordinate EGR operations with emission control operations. One example approach is illustrated by Arnold in US 2004/0050047 A1. Therein, a particulate filter is included in the EGR passage so that particulates may be removed from the EGR flow before exhaust gases are recirculated through the intake.
However, the inventors herein have recognized several potential issues with such an approach. As one example, to regenerate the filter, hot exhaust gas may have to be passed through the EGR passage. The heated EGR flow may, however, decrease the engine performance and increase fuel penalties. On the other hand, without the filter, and/or without filter regeneration, particulate matter recirculated into the intake with the EGR flow may cause compressor fouling and degrade engine performance.
In one example, the above mentioned issues may be addressed by a method of operating a turbocharged engine including a particulate filter positioned upstream of a turbocharger turbine, a catalyst positioned downstream of the turbine, and an EGR passage coupled between an engine exhaust and engine intake. In one embodiment, the method comprises, diverting exhaust gas from downstream of the filter to the engine intake via the EGR passage; and adjusting an amount of diverted exhaust gas based on filter operating conditions.
In this way, by adjusting EGR based on filter operation, it is possible to reduce EGR recirculation, if needed, during filter regeneration. By positioning the particulate filter upstream of the turbocharger turbine and upstream of an EGR passage inlet, both EGR and particulate filter benefits may be achieved. Specifically, as noted above, when EGR is desired, exhaust gas may be recirculated through the EGR passage after passing through the filter, thereby providing a clean EGR flow to the intake and reducing compressor degradation. Then, when filter regeneration is desired, heated exhaust may be passed through the filter but may not be recirculated (or may be recirculated to a lesser degree) through the EGR passage, thereby reducing engine performance degradation due to hot EGR flow. Furthermore, by reducing the amount of hot exhaust that is recirculated to the engine intake during filter regeneration, the thermal demands on an EGR cooler may also be reduced, thereby providing engine additional engine performance and fuel economy benefits.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.